Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$224.67	11.641%	$250.8238	$250.82	$250.80	$250.80
Purchase #2	$217.43	3.431%	$224.89	$224.89	$224.90	$224.90
Purchase #3	$169.69	11.430%	$189.0856	$189.09	$189.10	$189.10
Purchase #4	$141.88	9.443%	$155.2777	$155.28	$155.30	$155.30
Purchase #5	$9.83	5.706%	$10.3909	$10.39	$10.40	$10.40
Purchase #6	$199.44	3.373%	$206.1671	$206.17	$206.15	$206.20
Purchase #7	$127.57	11.457%	$142.1857	$142.19	$142.20	$142.20
7 purchase totals =	$1,090.51		$1,178.8208	$1,178.83	$1,178.85	$1,178.90